Assembly for indicating translational movement of a member selectively in one of two scales

Abstract

An assembly for attachment to a rotatable shaft of a machine tool, for example, a lathe, for indicating translational movement of a member selectively in one of two scales, including two dials graduated one in each said scale, an idler pinion connecting the two dials, the number of teeth on each dial engaging the idler pinion giving the required conversion ratio, and an indexable sleeve surrounding both dials and being movable to reveal only a selected scale at any one time.

What we claim is: 
     
       1. An assembly for indicating translational movement of a member selectively in one of two scales, including a sub-assembly adapted for mounting on a fixed structure, a first dial for mounting coaxially with and for rotation about a shaft, a second dial for mounting coaxially with and for rotation about said shaft, said first and second dials both having internal teeth in mesh with an idler pinion carried by said sub-assembly, said first and second dials also having a first and second set of graduations marked respectively on the external surfaces thereof as continuing scales (as herein defined), and an indexable sleeve surrounding both of said scales, said sleeve being rotatable about the axis of said shaft and having two openings therein through which the graduations may be observed and read against a datum line associated with each opening, said openings being positioned so that only one thereof is in view from a given direction at any one time to observe the respective scale, said first dial being connectable for rotation by said shaft and said second dial being rotated by rotation of said first dial through said idler pinion, the number of teeth on the first and second dials being such as to give the desired conversion ratio from one said scale to the other. 
     
     
       2. An assembly as claimed in claim 1, in which said first dial is in screw-threaded connection with a lock nut for zero setting purposes. 
     
     
       3. An assembly as claimed in either claim 1 in which said sleeve has its openings disposed at 180° to each other about said shaft and a detent mechanism is provided to retain the sleeve temporarily in its two locations. 
     
     
       4. An assembly as claimed in claim 3, in which said detent mechanism includes two balls in the sub-assembly which engage selectively in two holes in an end plate integral with the sleeve and resilient means is provided to urge the plate against the balls. 
     
     
       5. An assembly as claimed in claim 4, in which the said resilient means is a Belleville spring. 
     
     
       6. An assembly as claimed in claim 1 for converting movement of said member from Imperial to metric units or vice versa, in which said first dial is provided with 127 gear teeth and said second dial is provided with 125 or 120 gear teeth depending on whether the screw pitch involved is in multiples of 0.100 inches or 0.125 inches, respectively. 
     
     
       7. An assembly as claimed in claim 1 when fitted to a machine tool by operatively connecting said first dial for rotation with a shaft of said machine tool.